LDCP

Transparent Data Latch with Asynchronous Clear and Preset

LDCP is a transparent data latch with data (D), asynchronous clear (CLR) and preset (PRE) inputs. When CLR is High, it overrides the other inputs and resets the data (Q) output Low. When PRE is High and CLR is low, it presets the data (Q) output High. Q reflects the data (D) input while the gate (G) input is High and CLR and PRE are Low. The data on the D input during the High-to-Low gate transition is stored in the latch. The data on the Q output remains unchanged as long as G remains Low.

The latch is asynchronously cleared, output Low, when power is applied. Virtex and Spartan2 simulate power-on when global set/reset (GSR) is active. GSR defaults to active-High but can be inverted by adding an inverter in front of the GSR input of the STARTUP_SPARTAN2 or STARTUP_VIRTEX symbol.

Inputs				Outputs
CLR	PRE	G	D	Q
1	X	X	X	0
0	1	X	X	1
0	0	1	1	1
0	0	1	0	0
0	0	0	X	No Chg
0	0		D	d
d = state of input one setup time prior to High-to-Low gate transition